Hospitals have been ordered to change the way they use a substance that is regularly used to treat critically ill patients.

It follows reports that potassium chloride killed three people after being administered wrongly in a handful of NHS trusts over a six-month period.

The discovery came out of the first-ever detailed study of "adverse incidents" - situations in which patients have been placed at risk in NHS hospitals - a report it has been claimed the government was trying to cover up.

In its first NHS alert, the National Patient Safety Agency (NPSA) has ordered hospitals to withdraw potassium chloride from all general wards in its neat form.

Trusts in England and Wales have been told to replace it with a diluted form of the solution.

Tight controls

Further controls are to be introduced in specialist wards while manufacturers will have to introduce changes to the way they produce and package potassium chloride.

The substance, which is used in some parts of the United States to execute prisoners on death row, is used in small doses to treat critically ill patients who have dangerously low levels of potassium.

However, a pilot study carried out by the NPSA has found that the substance had been administered wrongly in 31 cases and caused three deaths.

This is believed to have been caused by confusion over packaging and labelling of the product with potassium chloride mistaken for saline.

Sir Liam said the decision would save lives

Professor Sir Liam Donaldson, chief medical officer for England, said the alert was part of a new approach to patient safety in the NHS.

"What we have started to do is to take safety really seriously for the first time but more than that to take action on some of the things which perhaps in the past have been neglected," he said.

"Our plan is to remove the concentrated solution from the more dangerous areas where it may be inadvertently used and that is the sort of early action which will quite literally save lives."

These mistakes were among 27,000 "adverse incidents" identified in the NPSA study in just 28 NHS trusts over a six month period.

Some of those were relatively trivial problems, such as a bandage being wrongly applied or a patient tripping, but others were classified as "catastrophic".